The present invention relates to a device for the insertion of the filling thread by means of a jet of fluid on a loom. The device comprises a reciprocating pump for the drawing in of fluid and the pumping out of said fluid into a filling thread insertion nozzle, a spring operatively connected with the piston of the reciprocating pump to produce the discharge stroke of the piston, a driven cam, a feeler roller operatively cooperating with said cam and a transmission mechanism between the feeler roller and the piston of the reciprocating pump in order to bring about the suction stroke of the piston in opposition to the action of the spring.
In such a device it is necessary that the quantity of fluid pumped by the discharge stroke of the piston of the reciprocating pump be correctly dimensioned for each filling thread insertion in accordance with the textile requirements, such as, type of filling thread material, width of loom, operating speed, and the like. The amount of fluid delivered per discharge stroke must therefore be capable of being changed. Replacement of the cam or the reciprocating pump or its pistons would be too difficult and time consuming. It is therefore already known to change the amount of fluid pumped per discharge stroke by providing an adjustable stop in order to limit the discharge stroke of the reciprocating pump which takes place under the action of the spring. In this way the result is obtained that upon each discharge stroke a part of the content of the pump which lies between zero and the maximum displacement of the pump has been delivered. This type of regulation of the delivery, however, has a number of disadvantages, namely:
The stop which shortens the length of the stroke has the result that the feeler roller, each time that it strikes the stop, periodically lifts itself off of the cam and the cam subsequently comes against the lifted feeler roller, whereby an undesired amount of noise and excessive wear of the feeler roller and of the cam are caused. Since the suction stoke of the reciprocating pump is caused, depending on the adjustment of the stop, by means of a longer or shorter portion of the ascending part of the cam, the duration of the suction stroke, in case of constant speed of rotation of the cam, is dependent on the adjustment of the stop. As long as the feeler roller has been lifted by the stop from the cam, the reciprocating pump remains at rest, and this period of time is not utilized for the operation of the pump nor drawing in of fluid. As soon as the cam comes against the raised feeler roller, the suction stroke is directly commenced whereby a vacuum is produced in the pump chamber since the fluid cannot flow sufficiently rapidly into the pump. The formation of this vacuum leads to undesired eddying on the part of the inward flowing fluid, and, if the fluid is a liquid, to partial evaporation of the liquid and thus to the production of gases in the pump chamber. In neither case does the volume of fluid drawin into the pump correspond precisely to the volume of the pump chamber. Upon the following discharge stroke of the piston therefore, instead of the desired quantity of fluid being discharged, there is discharged a smaller quantity which varies in indefinite manner so that the insertion of the filling thread takes place in nonuniform fashion and in some cases even defectively.